Silencing cholera's social media

May 24, 2016

Bacteria use a form of "social media" communication called quorum sensing to monitor how many of their fellow species are in the neighborhood, allowing them to detect changes in density and respond with changes in collective behavior. Because of the importance of quorum sensing to the behavior of disease-causing bacteria like Vibrio cholerae, the cause of the deadly disease cholera, understanding how it works has the potential to allow us to disrupt it for therapeutic purposes.

Quorum sensing involves bacteria secreting small signaling molecules called autoinducers that are detected by receptors located in other bacteria; these receptors then trigger intracellular responses via downstream signaling proteins called response regulators. In a new study, researchers led by Frederick Hughson and Bonnie Bassler at Princeton University, publishing in the open access journal PLOS Biology this week, now tease apart the molecular mechanism whereby one of these response regulators, LuxO, regulates the pathogenicity of V. cholerae.

LuxO, like many other members of the AAA+ ATPase superfamily of proteins, was expected to form a doughnut-shaped structure made of six molecules. The active form (but not the inactive form) of LuxO was already known to bind to specific target genes, activating their transcription, but it was not known how the phosphorylation of LuxO by quorum-sensing receptors regulated this activity. With a combination of X-ray crystal structures, and functional testing of judiciously engineered LuxO molecules, the authors of this study now show how this happens.

Each individual LuxO molecule is made of three domains; an N-terminal receiver (R) domain, a central catalytic (C) ATPase, and a C-terminal DNA-binding (D) domain. In their study, the researchers determined the crystal structure of a version of LuxO from the related bacterium V. angustum that lacks the D domain, finding that the C domain forms the expected doughnut shape with C domains of five other LuxO molecules, and that the R domains sit on the outside of this ring.

However, the authors noticed an unusual linker segment between the R and C domains; in the inactive state, when the R domain is unphosphorylated, this linker and part of the R domain physically block the active catalytic site in the C domain. Mutating the linker or the interface between the R and C domains prevented this inhibition from happening, resulting in a LuxO molecule that was permanently switched "on." Comparison with other closely related AAA+ ATPase proteins suggests that the internal molecular movements that usually accompany R domain phosphorylation would also relieve this inhibition, with the R domains swinging out to liberate the LuxO ATPase catalytic site -- a pre-requisite for activating transcription of target genes (see image).

The intriguing inhibitory mechanism revealed by this study is an entirely novel mechanism of AAA+ protein regulation, and opens the door for pharmacological interference. The prominent position of LuxO in the quorum-sensing cascade and the fact that it is found in many vibrio species makes it a particularly attractive target for drugs that might treat cholera and diseases caused by related bacteria. As proof of principle, the authors also analysed the mechanism of action of a small-molecule inhibitor of V. cholerae virulence called AzaU that they had previously identified. They show that AzaU also binds to the active site of LuxO, mimicking aspects of the autoinhibitory mechanism and turning off the production of virulence factors.
-end-
In your coverage please use this URL to provide access to the freely available article in PLOS Biology: http://dx.plos.org/10.1371/journal.pbio.1002464

Citation: Boyaci H, Shah T, Hurley A, Kokona B, Li Z, Ventocilla C, et al. (2016) Structure, Regulation, and Inhibition of the Quorum-Sensing Signal Integrator LuxO. PLoS Biol 14(5): e1002464. doi:10.1371/journal.pbio.1002464

Funding: CHESS is supported by the NSF and NIH/NIGMS via NSF award DMR-1332208, and the MacCHESS resource is supported by NIGMS award GM-103485. Work in our labs was supported by the Howard Hughes Medical Institute (HHMI), NIH (AI054442, AI091681, and GM065859), and NSF (MCB-0343821). BLB is an investigator of the HHMI. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

PLOS

Related Bacteria Articles from Brightsurf:

Siblings can also differ from one another in bacteria
A research team from the University of Tübingen and the German Center for Infection Research (DZIF) is investigating how pathogens influence the immune response of their host with genetic variation.

How bacteria fertilize soya
Soya and clover have their very own fertiliser factories in their roots, where bacteria manufacture ammonium, which is crucial for plant growth.

Bacteria might help other bacteria to tolerate antibiotics better
A new paper by the Dynamical Systems Biology lab at UPF shows that the response by bacteria to antibiotics may depend on other species of bacteria they live with, in such a way that some bacteria may make others more tolerant to antibiotics.

Two-faced bacteria
The gut microbiome, which is a collection of numerous beneficial bacteria species, is key to our overall well-being and good health.

Microcensus in bacteria
Bacillus subtilis can determine proportions of different groups within a mixed population.

Right beneath the skin we all have the same bacteria
In the dermis skin layer, the same bacteria are found across age and gender.

Bacteria must be 'stressed out' to divide
Bacterial cell division is controlled by both enzymatic activity and mechanical forces, which work together to control its timing and location, a new study from EPFL finds.

How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.

The bacteria building your baby
Australian researchers have laid to rest a longstanding controversy: is the womb sterile?

Hopping bacteria
Scientists have long known that key models of bacterial movement in real-world conditions are flawed.

Read More: Bacteria News and Bacteria Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.